The present invention is directed to a surgical method for treating presbyopia and to the associated devices to be used in conjunction with the method.
Presbyopia is the nearsightedness associated with aging resulting from the failure of the accommodation mechanism of the eye. The accomodative mechanism is driven principally by parasympathetic innervation of the ciliary smooth muscle. This causes the muscle to slide forward in a unified manner and produces an inward movement of the muscle. The result is a reduction in the diameter of the ciliary muscle collar that instigates a series of events leading to an ability to see near objects clearly.
While it is clear that the capsular elasticity of the lens of the eye, i.e., the ability of the lens capsule to mold the lens, diminishes with age, the precise cause of presbyopia remains the subject of debate.
Presbyopia is most frequently treated by the use of reading glasses, bifocals, and progressive multi-focal contact lenses. However, the inconveniences associated with eyeglasses and contact lenses have prompted investigation into, and the development of, surgical techniques aimed at correcting presbyopia.
One such method is anterior ciliary sclerotomy (xe2x80x9cACSxe2x80x9d). ACS is based on the theory that accommodation results primarily from ciliary body contraction, with the resulting forward movement of the lens. Its underlying rational is based on the observation that the lens constantly grows throughout life, gradually crowding the posterior chamber and eventually preventing full function of the ciliary body/zonular complex. The xe2x80x9ccrowdedxe2x80x9d state causes the reduction of lens power change with attempt at accommodation. ACS utilizes a series of symmetrical radial, partial-thickness scleral incisions to attempt to make more room for the ciliary bodyxe2x80x94which in turn allows more space for the lensxe2x80x94by expanding the globe in the area of the ciliary body. However, this procedure has many potential complications, ranging from infection and hemorrhaging to perforation, which could result in retinal detachment, iris injury or prolapse.
Another proposed method for surgical reversal of presbyopia is based on the theory that presbyopia results when the distance between the ciliary body and the equator of the lens and its capsule becomes less with age as a result of the normal growth of the lens. Thus, under this theory presbyopia is treated by increasing the effective working distance of the ciliary muscle. This is accomplished by implanting a series of scleral expansion bands just below the surface of the sclera and outside the cornea. The bands stretch the sclera so that the diameter of the circle describing the intersection of the plane of the ciliary body with the sclera is slightly increased. See, U.S. Pat. Nos. 5,354,331 and 5,489,399 to Schachar. However, at least one study has called into question the accuracy of the theory on which scleral expansion surgery is premised. See, Mathews, xe2x80x9cScleral Expansion Surgery Does Not Restore Accommodation in Human Presbyopia,xe2x80x9d Opthamology, Vol. 106, No. 5, May, 1999, pages 873-877. This study concludes that, if scleral expansion surgery does alleviate presbyopia, an explanation other than the restoration of accommodation needs to be found.
Regardless of the theory employed, there is a need for correcting presbyopia without the use of eyeglasses or contact lenses through a relatively safe and simple procedure that is easily reversible.
Accordingly, it is the principle object of the present invention to provide a surgical method for correcting presbyopia.
It is a further object to provide such a method that has a reduced potential for complications and is easily reversible.
It is a still further object of the invention to provide a clip uniquely suited for use in the treatment of presbyopia.
These objects, as well as others which will become apparent upon reference to the following detailed description and accompanying drawings, are accomplished by a method for treating presbyopia in which the sclera is supported or reinforced, while the spatial relationship between the ciliary muscle and the lens is substantially unchanged. Specifically, the method includes making an incision in the conjunctiva to gain access to the sclera overlying the ciliary muscle. The Tenon""s capsules are moved laterally to expose the sclera, and the sclera is extended outwardly. A clip, or series of clips, is provided having two closeable arms for grasping the outwardly-extended sclera therebetween. The arms of the clip are closed on the sclera so as to engage a portion of the sclera, and then the Tenon""s capsules are slid over the clip and the conjunctiva is closed. Preferably, four such scleral clips are applied to the sclera substantially equally spaced about the lens between the medial, inferior, lateral and superior rectus muscles. When applied to the sclera, the clips serve to prevent the sclera from buckling under tension applied by the ciliary muscle when trying to accommodate the eye to near vision.
In another aspect of the invention, a scleral clip is provided for applying to the sclera. The clip comprises two arms relatively moveable with respect to each other from an open position to a closed position. The clips have a length of no longer than approximately 5.0 to 6.0 mm so as to fit between adjacent rectus muscles. The arms may also be provided with means, such as teeth or spurs, for graspingxe2x80x94but not penetratingxe2x80x94the sclera. The arms of the clip remain in the closed position in the absence of an external force applied therebetween.